Solid state silicon-based condenser microphone

ABSTRACT

A solid state silicon-based condenser microphone comprising a silicon transducer chip ( 1 ). The transducer chip includes a backplate ( 13 ) and a diaphragm ( 12 ) arranged substantially parallel to each other with a small air gap in between, thereby forming an electrical capacitor. The diaphragm ( 12 ) is movable relative to the backplate ( 13 ) in response to incident sound. An integrated electronic circuit chip ( 3 ) or ASIC is electrically coupled to the transducer chip ( 1 ). An intermediate layer ( 2 ) fixes the transducer chip ( 1 ) to the integrated electronic circuit chip ( 3 ) with the transducer chip ( 1 ) on a first side of the intermediate layer ( 2 ) and the integrated electronic circuit chip ( 3 ) on a second side of the intermediate layer ( 2 ) opposite the first side. The intermediate layer ( 2 ) has a sound inlet ( 4 ) on the same side as the ASIC giving access of sound to the diaphragm.

RELATED APPLICATIONS

Notice: More than one reissue application has been filed for the reissueof U.S. Pat. No. 6,088,463. This application is a divisional of U.S.patent application Ser. No. 10/193,055, entitled “Solid StateSilicon-Based Condenser Microphone,” which was filed on Jul. 11, 2002,which is a reissue U.S. Pat. No. 6,088,463, issued on Jul. 11, 2000,which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

This invention related to miniature condenser microphones, and inparticular to solid state silicon-based condenser microphonesincorporating an integrated electronic circuit for transducer signalconditioning. Such miniature microphones are suitable for use inminiature electroacoustic devices such as hearing instruments.

BACKGROUND OF THE INVENTION

In the hearing instruments industry one of the primary goals is to makehearing instruments of small size while still maintaining goodelectroacoustic performance and operability giving good userfriendliness and satisfaction. Technical performance data comprise suchas sensitivity, stability, compactness, robustness and insensitivity toelectromagnetic interference and to other external and environmentalconditions. In the past, several attempts have been made to makemicrophones smaller while still maintaining good technical performancedata.

EP 561 566 discloses a solid state condenser microphone having atransducer chip and, on the same chip, an electronic circuit and acavity forming an opening or sound inlet for the transducer. Thetechniques and processes for manufacturing such electronic circuitry arequite different from the techniques and processes used in manufacturingthe transducer elements. Consequently a chip having both an electroniccircuit and an opening therein requires two (or possibly more) separatestages of production, usually at different facilities.

SUMMARY OF THE INVENTION

The invention provides a solid state silicon-based condenser microphonewhich is suitable for batch production. Several silicon chips arestacked, and the subsequent dicinig of the stacked chips or discs iseasier than with the prior art.

The invention makes it possible to make a very well defined sound inlet,which can optionally be covered with a sealing film or a filterpreventing dust, moisture and other impurities from contaminating orobstructing the interior and the sound inlet of the microphone. A soundinlet can theoretically be made as an opening in any of the chipsurfaces including the fractures after dicing, but in practice thefractures are irregular surfaces and therefore less suitable forsupporting a sealing film or a filter, since the irregular fracturescould give rise to the sealing film or a filter becoming wrinkled andhaving leakages at its periphery where it is secured to the die surface.A microphone according to the invention has an opening forming a soundinlet in the practically perfectly flat and polished faces of the waferon which several individual microphones are arranged.

An integrated electronic circuit chip can be arranged on the same planesurface, which is perfectly suited for flip-chip mounting the electroniccircuit chip.

An intermediate chip is arranged between the electronic circuit chip andthe transducer chip. The intermediate chip has another opening withfeedthrough electrical connections on a surface of the opening. Thefeedthrough connections establish electrical connections between thetransducer element on the transducer chip and the electronic circuitchip. This gives a high degree of freedom in designing both thetransducer chip and the electronic circuit chip and in particular theirelectrical terminations.

External electrical connections can be established economically andreliably, and thermal stresses can be avoided with the small size solidstate silicon-based condenser microphone of the invention.

The invention uses a separate integrated electronic circuit chip,preferably a CMOS ASIC (Application Specific Integrated Circuit) whichcan be designed and manufactured separately and independent of thedesign and manufacture of the transducer portion of the microphone. Thisis advantageous since the techniques and processes for manufacturingintegrated electronic circuit chips are different from those used inmanufacturing transducer elements, and each production stage can thus beoptimized individually and independent of each other.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be explained with reference to thedrawings, in which:

FIG. 1 is a cross section of a microphone according to the invention,and

FIG. 2 is an enlarged view of a portion of the microphone in FIG. 1.

In the figures, for illustrative purposes, dimensions such as materialthickness and mutual distances and possibly other proportions are notnecessarily drawn to the same scale.

DETAILED DESCRIPTION OF THE INVENTION

The illustrated microphone has the following structure. A silicontransducer chip 1 with a central opening etched therein carries adiaphragm 12 and a backplate 13 covering the central opening in thetransducer chip. In this context the term “backplate” means a structuralelement which is relatively rigid as compared to the associateddiaphragm, which in turn is relatively moveable. The backplate can beplaced on either side of the diaphragm. The transducer chip with thediaphragm 12 and a backplate 13 are preferably manufactured as describedin The copending Danish patent application PA 199800671. The transducerchip 1 and a backchamber-chip 17 having a cavity etched therein, andtogether the transducer chip 1 and the backchamber-chip 17 form a closedbackchamber 11 with the diaphragm 12 forming one wall of the backchamber11. The diaphragm 12 and the backplate 13 are both electricallyconductive or semi-conductive and are arranged parallel and in closeproximity to each other and with a well defined air gap in between, sothat they form an electrical capacitor.

The backplate 13 has a plurality of perforations 19 making itacoustically transparent, and the diaphragm has a tiny vent hole 15 forequalising the static pressure on both sides of the diaphragm.

An electronic circuit chip 3 having an integrated circuit on a surfacethereof is flip chip mounted with its circuit facing the transducer chip1 and with an intermediate chip 2 between the transducer chip 1 and theelectronic circuit chip 3. The intermediate chip 2 has a cavity 10 and afirst through going opening 4 and a second through going opening 18 bothcommunicating with the cavity 10. The intermediate chip 2 is secured tothe transducer chip 1 by means of an electrically conductive solder ring9 or by other means.

The electronic circuit chip 3 is secured to the intermediate chip 2 bymeans of an underfill material 6.

The diaphragm 12 and the backplate 13 are electrically connected Lorespective ones of solder bumps 8, which connect the diaphragm 12 andthe backplate 13 to electrical feedthrough conductors 14 on the surfaceof the cavity 10 and the opening 18 and further to the upper surface ofthe intermediate chip 2 where connections to the electronic circuit chip3 are established via a conventional flip-chip interconnect method e.g.gold studs 7 with conductive adhesive. This is most clearly seen in FIG.2.

The opening 4 is covered with a filter 5 or a flexible sheet ordiaphragm of acoustically transparent material. The whole structure isencapsulated in a polymer encapsulation 16 leaving the filter 5 free.

The function of the above described structure is as follows. The opening4 functions as a sound inlet, and ambient sound pressure enters throughthe filter 5 covering the opening 4 to the cavity 10 functioning as afront chamber for the microphone. Through the perforations 19 in thebackplate 13 the sound pressure reaches the diaphragm 12. The cavity 11functions as a backchamber for the microphone. The diaphragm 12 ismovable relative to the backplate 13 in response to incident sound. Whenthe diaphragm is moved in response to the incident sound, the electricalcapacity of the electrical capacitor formed by the diaphragm 12 and thebackplate 13 will vary in response to the incident sound. The circuit onthe integrated circuit chip 3 is electrically connected to the diaphragm12 And the backplate 13 via the electrical feedthrough conductors 14,and the circuit is designed to detect variations in the electricalcapacity of the capacitor formed by the diaphragm 12 and the backplate13. The circuit has electrical connections for electrically connectingit to a power supply and other electronic circuitry in eg a hearinginstrument.

In the illustrated embodiment the transducer element on the transducerchip is a condenser microphone with a diaphragm and a single backplate.In an alternative embodiment the transducer element has its diaphragmarranged between two backplates. Such a microphone can give balancedoutput signal which is less sensitive to electrical interference.

1. A solid state silicon-based condenser microphone comprising a silicontransducer chip (1) including a backplate (13) and a diaphragm (12)arranged substantially parallel to each other, thereby forming anelectrical capacitor, the diaphragm (12) being movable relative to thebackplate (13) in response to incident sound, an integrated electroniccircuit chip (3) electrically coupled to the transducer chip (1), anintermediate layer (2) fixing the transducer chip (1) to the integratedelectronic circuit chip (3) in a spaced relationship, with thetransducer chip (1) on a first side of the intermediate layer (2) andthe integrated electronic circuit chip (3) on a second side of theintermediate layer (2) opposite the first side, the intermediate layer(2) having a first through going opening (4, 10) between its first sideand its second side giving access of sound to the diaphragm.
 2. Acondenser microphone according to claim 1 wherein the intermediate layer(2) on a surface thereof has electrical conductors (14) electricallyconnecting the transducer chip (1) to the integrated circuit chip (3).3. A condenser microphone according to claim 2 wherein the intermediatelayer (2) has a second through going opening (18) with a surface onwhich the electrical conductors (14) electrically connecting thetransducer chip (1) to the integrated circuit chip (3) are situated. 4.A condenser microphone according to claim 1 wherein the opening (4) inthe intermediate layer is covered with a film (5) sealing the opening(4) on the second side of the intermediate layer (2).
 5. A condensermicrophone according to claim 1 wherein a cavity (11) is provided in thetransducer chip (1) on a side of the diaphragm (12) opposite theintermediate layer (2).
 6. A condenser microphone according to claim 5wherein the cavity (11) is a closed cavity.
 7. A condenser microphoneaccording to claim 2 wherein the integrated electronic circuit chip (3)has a surface including electronic circuits with said surface facing theintermediate layer (2).
 8. A condenser microphone according to claim 1wherein the intermediate layer (2) is a silicon-based chip.
 9. Asilicon-based electroacoustic transducer, comprising: a silicon-basedtransducer chip for transducing between acoustic signals and electricalsignals, wherein said silicon-based transducer chip includes a backplateand a diaphragm; a silicon-based integrated electronic circuit chip; andan intermediate element secured to said silicon-based transducer chipand to said integrated electronic circuit chip, said intermediateelement including an electrical conductor electrically coupling saidintegrated electronic circuit chip and said transducer chip, saidelectrical signals being transmitted along said electrical conductor.10. The silicon-based electroacoustic transducer of claim 9, whereinsaid silicon-based integrated electronic circuit chip is an ASIC chip.11. The silicon-based electroacoustic transducer of claim 9, whereinsaid silicon-based integrated electronic circuit chip is flip-chipmounted to said intermediate element.
 12. The silicon-basedelectroacoustic transducer of claim 9, wherein said intermediate elementincludes a feed-through, said feed-through including a feed-throughconductor leading to said silicon-based integrated electronic circuitchip.
 13. The transducer of claim 9, wherein the intermediate elementhas a first surface and a second surface opposing said first surface,said silicon-based transducer being mounted to said first surface, saidintermediate element further including an acoustic port on said secondsurface leading to an acoustic passage extending to said first surfaceof said intermediate element, said acoustic passage for transmittingsaid acoustic signals to said transducer chip mounted on said firstsurface of said intermediate element; and a filter adjacent to saidacoustic port for preventing contamination of said acoustic passage. 14.The transducer of claim 9, wherein the integrated electronic circuitchip has an integrated circuit on a surface thereof.